Project 3 (P3): ABSTRACT Basic, translational and clinical studies attest to the pivotal role of plasminogen in numerous physiological and pathophysiological responses. In many of these processes, the involvement of plasminogen arises from its influence on inflammatory cell recruitment, which in turn depends upon its interaction with plasminogen receptors (Plg-Rs) on the responding cells. Examples of responses involving inflammatory cell recruitment in which plasminogen and Plg-Rs have been implicated include peritonitis, sepsis, lung injury, angiogenesis, restenosis, and mobilization of hematopoietic progenitor stem cell following myocardial infarction. On macrophages, Plg-Rs are heterogeneous and include ones with (tailed Plg-Rs) and without transmembrane domains (tailless Plg-Rs). The major tailless Plg-Rs are histone H2B, annexin2, p11 and ?-enolase, and the major tailed Plg-Rs are ?M?2 and PlgR-KT. A unique panel of blocking antibodies to these six major Plg-Rs has been assembled that can be administered in vivo as Fab fragments to inhibit inflammatory responses. In Aim 1, these reagents, in combination with over-expression and mutagenesis strategies, will be used to allow the first objective dissection of the contribution of individual Plg-Rs in biologically relevant inflammatory responses to test the hypothesis that Plg-Rs are utilized in cellular recruitment in a stimulus and tissue specific manner. The tailless Plg-Rs reach the cell surface through a common mechanism involving calcium mobilization via L-type calcium channels, but the mechanism by which they tether to the cell surface is unresolved. As part of Aim 1, mechanisms, tethering to phosphatdylserine and trafficking to lipid rafts, by which tailless Plg-Rs reach and anchor to the macrophage surface will be identified. Aim 2 will focus on the unexpected discovery that plasminogen controls macrophage uptake of oxidized lipoproteins to form foam cells and regulates expression of a number of proatherogenic genes in these cells. The Plg-Rs that mediates this novel plasminogen-dependent pathway of foam cell formation (p-FCF), the transmembrane co-receptor that is necessary to transduce intracellular signaling to regulate this pathway, the lipid requirements for plasminogen to regulate gene expression, and the relationship of p-FCF to the GAIT pathway of gene regulation in macrophages will be analyzed in collaboration with Projects 1 and 2 of the Program. We have recently discovered that plasminogen markedly enhances macrophage phagocytosis. In Aim 3, we will specifically focus on how Lp(a), a close molecular mimic of plasminogen and a known cardiovascular risk factor, influences plasminogen-dependent foam cell formation and the pathocytotic pathways, two responses that may exert opposing effects on the development of atherosclerotic lesions. Taken together, these studies will define how plasminogen and its receptors function in inflammation and cardiovascular disease.